Targets and processes for fabricating same

ABSTRACT

In one embodiment, the present disclosure provides a target or mold having one or more support arms coupled to a substrate. The support arm can be used in handling or positioning a target. In another embodiment, the present disclosure provides target molds, targets produced using such molds, and a method for producing the targets and molds. In various implementations, the targets are formed in a number of disclosed shapes, including a funnel cone, a funnel cone having an extended neck, those having Gaussian-profile, a cup, a target having embedded metal slugs, metal dotted foils, wedges, metal stacks, a Winston collector having a hemispherical apex, and a Winston collector having an apex aperture. In yet another embodiment, the present disclosure provides a target mounting and alignment system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/319,592, filed Jun. 30, 2014, which is a divisional application ofU.S. patent application Ser. No. 12/918,292, filed Aug. 18, 2010, nowabandoned, which in turn is the U.S. National Stage of InternationalApplication No. PCT/US2009/034527, filed Feb. 19, 2009, which waspublished in English under PCT Article 21(2), which in turn claims thebenefit of U.S. Provisional Patent Application Nos. 61/029,909 filedFeb. 19, 2008; 61/030,941, filed Feb. 22, 2008; 61/030,942, filed Feb.23, 2008; and 61/030,945, filed Feb. 23, 3008. Each of theseapplications is incorporated by reference herein in its entirety.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Grant No.DE-FC52-01NV14050 awarded by the Department of Energy. The governmenthas certain rights in the invention.

TECHNICAL FIELD

The present disclosure relates to targets and their methods offabrication. In particular examples, the present disclosure providemethods of fabricating metal targets useable as laser targets inhigh-energy laser-physics.

BACKGROUND

Metal covered targets are typically used in high energy physicsapplications. For examples, such targets may be shot with a laser inorder to generate plasmas or high energy radiation. Such targets may beused in applications such as inertial confinement fusion.

Laser targets used to produce plasma and radiation typically havedisadvantages. For example, such targets are typically manufacturedindividually and thus can be comparatively expensive. The expense of thetargets may limit the number of targets available for use, thuspotentially limiting how the targets can be used. For example, a limitednumber of targets available for a series of experiments may limit thequality or quantity of data obtained during the experiments.

In addition, laser targets typically require great care in handling andmounting, which can be time consuming and further limit how the targetsmay be used. For example, difficulties in mounting and handling targetscan preclude uses that require rapid sequential target irradiation.

The comparatively large size of prior targets, and surfaceirregularities, may interfere with full characterization of the producedplasma. Excessive target material may also interfere with optimal energyproduction.

Some prior experiments have used metal coated silicon targets. However,the silicon included in such targets typically interferes with energyfocusing and radiation enhancement.

SUMMARY

As described in more detail below, various aspects of the presentdisclosure provide molds and metal shapes formed using such molds thatcan be used, for example, as laser targets. For example, the targets maybe used for fusion applications, plasma generation, or generating othertypes of energy or particles. The metallic portion of the targets may beformed from various metals. Some embodiments of the targets use a singlemetal. Other embodiments use multiple metals. When multiple metals areused, the thickness, pattern, and relative order of the metals may bevaried as desired. Suitable metals include Au, Al, Pt, Fe, Ge, Cr, V,Cu, Pd, Ta, Ag, Ti, and W.

In one aspect, the present disclosure provides a silicon mold that, whencoated with one or more metals, produces a target that is conicallyshaped with a long neck profile. The present disclosure also providestargets made from such molds, including free-standing metal targets. Inone implementation, the mold produces a free-standing silicon nitridetarget.

One method for making the disclosed funnel cone molds and targetsinvolves depositing silicon dioxide and silicon nitride layers on thefront and back sides of a substrate, such as a silicon wafer. A layer ofphotoresist is applied to the front side and patterned to form windowsaround an island of silicon nitride/silicon dioxide. The silicon nitrideand silicon dioxide beneath the windows is etched away. A large windowis patterned and etched in a similar manner on the back side of thesubstrate. The substrate beneath the front windows is removed using anisotropic etch to produce a capped cone structure. The cap is removedand the front side of the substrate is coated with one or more metals.The substrate beneath the back side window is then removed.

In further aspects, the long neck cone molds or targets described abovehave extended long neck profiles. According to one method ofmanufacturing such molds and targets, silicon dioxide layer is formed onthe front and back sides of a substrate, such as a silicon wafer.Photoresist layers are deposited on the front and back sides. Windowssurrounding a central island of silicon dioxide are opened on the frontside. A larger window is opened on the back side. The silicon dioxidebeneath the front and back side windows is etched away. A cone structureis formed under the central island on the front side by isotropicallyetching the substrate beneath the windows. The overhanging region ofsilicon dioxide above the central island over the cone is then etchedaway. The front side is then anisotropically etched to extend the lengthof the neck of the cone structure. One more or metals are deposited onthe front side of the substrate. The substrate under the back sidewindow is removed.

In another aspect, the present disclosure provides a silicon mold that,when coated with one or more metals, produces a target that has aGaussian-like cross section. The present disclosure also providestargets made from such molds. In particular examples, the target hasmultiple metal layers.

According to one disclosed method of making Gaussian-shaped molds andtargets, silicon nitride and silicon dioxide layers are formed on frontand back sides of a substrate, such as a silicon wafer. Photoresistlayers are deposited on the front and back side, patterned, developed,and etched to form a large window in the back side siliconnitride/silicon dioxide layers and windows defining a central island ofsilicon nitride/silicon dioxide on the front side of the substrate. Thesubstrate beneath the front side windows is then etched. In a particularexample, the etch is an anisotropic etch and produces cavities, and acentral pillar, having generally linear sides. The pillar is thenrounded using a suitable etch, such as an HNA etch. The etch iscontinued until the pillar has the desired shape. In another example,the etch is a more isotropic etch and produces cavities and a centralpillar having curved sides. The pillar is then rounded using a suitableetch, such as an HNA etch. Regardless of the etch selected, once therounded pillar has been formed, one or more metal layers are depositedon the front side of the substrate. The substrate above the backsidewindow is then removed.

Further aspects of the present disclosure provide support structures,such as a cantilever, having a mold or target located at an end. In amore specific example, the target is made of a metal. In anotherexample, the target has multiple metal layers. In anotherimplementation, the mold or target is supported by a single supportstructure. In another implementation, the mold or target is supported bymultiple support structures, such as two, three, or four cantilevers.The support structures may be made from an insulating material, forexample, silicon nitride. In some implementations, the target or mold isattached to a handling die by a support structure, such as a cantilever,having a cross-section of less than about 15 μm², such as less thanabout 10 μm² or less than about 2 μm². In a particular example, thecross-section is about 1 μm².

In a further aspect, the present disclosure provides cup-shaped moldsand targets, including cup-shaped targets coupled to one or more supportstructures. The cup-shaped target is formed from a metal layer in someexamples. In other examples, the cup-shaped target has multiple metallayers.

According to one disclosed method of forming a cup-shaped target,silicon dioxide and silicon nitride layers are deposited on the frontand back sides of a substrate, such as a silicon wafer. Photoresistlayers are deposited on the front and back sides, patterned, developed,and etched to form windows defining a large central island in the backside silicon nitride/silicon dioxide layers and windows defining asmaller central island of silicon nitride/silicon dioxide in the frontside of the substrate. The photoresist layers are removed and a newphotoresist layer is deposited on the front side of the substrate andpatterned to form a window over at least a portion of the centralisland. The exposed silicon nitride, silicon dioxide, and substrateunder the central island is then etched to form a central cavity. Insome embodiments, this etch also defines a support structure, such as acantilever, connecting the cavity to the substrate. One or more metallayers are then deposited over the front side of the substrate. Themetal above the central cavity is covered with photoresist and theremaining, uncovered metal is removed. The substrate over the back sidewindows is then removed.

In another aspect, the present disclosure provides targets havingembedded metal slugs, including such targets located at the end of asupport structure, such as a cantilever. In a specific example, the slugis of a single metal, such as a single slug or multiple slugs of asingle metal. In other examples, the slug is a single slug havingmultiple metal layers or multiple metal slugs, at least one of which hasmultiple metal layers. In various examples, the slugs havecross-sections that are circular, square, or hexagonal.

One disclosed method of forming a target having embedded metal slugsinvolves depositing silicon nitride layers on the front and back sidesof a substrate, such as a silicon wafer. Photoresist layers aredeposited on the front and back sides, patterned, developed, and etchedto form windows defining a large central opening in the back sidesilicon nitride/silicon dioxide layers and windows defining a centralisland of silicon nitride/silicon dioxide in the front side of thesubstrate, located over the back side opening. The substrate over theback side opening is then removed. One or more metal layers aredeposited on the front side of the substrate. A photoresist layer isdeposited on the front side of the substrate and patterned to produce adesired feature, such as a single aperture or multiple apertures. One ormore metals are then deposited in the aperture or apertures. Thisprocess may be repeated, if desired. In some examples, a protectivelayer is deposited on the front side of the substrate prior to removingsubstrate from the back side. A layer of photoresist is deposited on theback side of the substrate, patterned, and developed to open a largewindow, the silicon nitride layer under the large window etched, and thesubstrate over the window removed. When a protective layer has beenused, it can then be removed.

Another embodiment of the present disclosure provides metal foils havingmetal dots formed thereon. According to one disclosed method, thesetargets are formed by depositing silicon dioxide and silicon nitridelayers on the front and back sides of a substrate, such as a siliconwafer. Photoresist layers are deposited on the front and back sides,patterned, developed, and etched to form a large back side window in thesilicon nitride and silicon dioxide layers and two silicondioxide/silicon nitride islands defined by windows in the front side ofthe substrate. One or more metal layers are deposited on the front sideof the substrate. Unwanted portions of the metal layer are removed and alayer of photoresist is deposited on the front side of the substrate andpatterned as desired, such as to produce desired dot shapes in a desiredpattern. One or metal layers are deposited on the front side of thesubstrate and then unwanted metal portions are removed. Substrate overthe back side window is then removed and, optionally, at least a portionof the silicon dioxide layer on the front side of the substrate.

In yet another example, the mold is suitable to produce a stack ofmetals located at the end of a support structure, such as a cantilever.The metal stack may have varying thicknesses or shapes. In anotherexample, the present disclosure provides a metal foil, which may havemultiple layers of different metals, spanned over a silicon die.

One embodiment of a method for forming a stacked metal target involvesdepositing silicon nitride on the front and back sides of a substrate,such as a silicon wafer. A photoresist layer is deposited on the frontside of the substrate, patterned, and developed to form a window in thephotoresist into which metals can be deposited. One or more metal layersare then deposited onto the front side of the substrate. Once thedesired metal layers have been deposited, in some embodiments, aprotective layer is formed on the front side of the substrate. A layerof photoresist is deposited on the back side of the substrate,patterned, developed, and etched to create a cavity under the front sidemetal layers and, optionally, define support structures, such aspillars, supporting at least a portion of the sides of the metal layers.

Another aspect of the present disclosure provides a metal foil targetthat is wedge-shaped. One disclosed method of preparing wedge targetinvolves depositing silicon nitride layers on the front and back sidesof a substrate, such as a silicon wafer. A photoresist layer isdeposited on the front side of the substrate, patterned, developed, andetched to define a central island of silicon nitride. The photoresist isremoved and another photoresist layer is applied to the front side ofthe substrate, patterned, and developed such that the central island isnot covered by photoresist. One or more metal layers are then depositedon the front side of the substrate. The metal over the photoresist isremoved. A photoresist layer is deposited on the back side of thesubstrate, patterned, developed, and etched to form a cavity under themetal layers and, optionally, define a support structure, such assupport pillars. The front side is then ground, such as with a die, toproduce a desired angle in the metal layers. In some cases, a protectivelayer is placed over the front side of the substrate. The remainingsubstrate in the back side cavity or cavities is then removed. When aprotective layer was used, it is then removed.

In another aspect, the present disclosure provides a mold that can beused to produce a target having a Gaussian-curved profile in the shapeof a Winston collector. The present disclosure also provides metaltargets having a Gaussian-curved profile in the shape of a Winstoncollector. In particular examples, the Winston collector has an apex anda hemisphere is located at the apex. In another example, the Winstoncollector has an apex and an aperture is formed in the apex.

According to one method of forming a Winston collector having ahemisphere at its apex, a photoresist layer is deposited on the backside of a substrate, such as a silicon wafer. The photoresist layer ispatterned, developed, and isotropically etched to form a hemisphericalcavity in the back side of the substrate. A silicon nitride layer isdeposited on the substrate and removed from the front side of the wafer,leaving the film on the back side only. Silicon dioxide layers are thendeposited to the front side of the substrate. A photoresist layer isdeposited on the front side of the substrate, patterned, developed, andetched to form a central window in the silicon dioxide layer. A cavity,such as a cavity having a Gaussian-like profile, is formed under thewindow, for example, using an isotropic etch. The silicon dioxide layeron the front side of the substrate is removed and one or more metallayers are deposited on the front side of the substrate. The silicondioxide layer on the back side of the substrate, and at least a portionof the substrate underlying the metal layer, are then removed.

One disclosed method of forming a Winston collector having a hole at itsapex involves coating the front and back sides of a substrate, such as asilicon wafer, with silicon nitride. A photoresist layer is deposited onthe front side of the substrate, patterned, developed, and etched toform a central window in the silicon nitride layer. The substrateunderneath the window is removed, such as using an isotropic etch, toproduce a cavity. A photoresist layer is deposited on the back side ofthe substrate, patterned, developed, and etched to form an apertureunderneath the apex of the front side cavity. One or more metal layersare then deposited on the front side of the substrate. The metal abovethe back side aperture is removed. The silicon nitride layer on the backside of the substrate is removed, followed by at least a portion of thesubstrate on the back side.

The present disclosure also provides an apparatus for mounting targets.In a particular example, the apparatus includes a silicon structurehaving one or more apertures. One or more targets, such as targetsattached to a handling die, can be located in each of the apertures. Thedepth, position, and orientation of the apertures can be used to controlthe relative alignment of the target or targets.

In one embodiment, a target mounting apparatus is formed by coating thefront and back sides of a substrate, such as a silicon wafer, withsilicon nitride. A photoresist layer is deposited on the front side ofthe substrate, patterned, developed, and etched to form one or morecavities in the silicon nitride and substrate into which targets can bemounted. The masking and etching process may be repeated, such as whencavities of different depths are desired.

In another aspect, the present disclosure provides a target manipulationapparatus. The target manipulation apparatus, in a particularimplementation, includes a mount for holding a wafer. The mount isrotatable. The mount is coupled to a xyz stage that translates the mountin space. In a more particular example, the mount and stage are manuallycontrollable. In another example, the mount and stage are coupled to acomputer and are controlled via software. The software, in someexamples, allows for manual control of the mount and stage. In otherexamples, the software allows for automated control of the mount andstage.

The present disclosure also provides a method for manipulating a target.The method includes providing a wafer, the wafer comprising a pluralityof targets. A first target of the plurality of targets on the wafer isplaced at a desired location, such as in the path of a laser. A secondtarget of the plurality of targets on the wafer is then placed at adesired location, such as in the path of a laser. In a particularexample, the first target is irradiated with the laser prior to thesecond target being placed at the desired location. In furtherimplementations, the wafer includes a first target type and a secondtarget type. The method includes selecting a target of a first type asthe first target. In a more particular example, the method then includesselecting a target of the second type as the second target.

In another aspect, the present disclosure provides targets having aconductive lead or a piezoresistive material. In a particularimplementation, the target includes both a conductive lead and apiezoresistive material. In one example, the target is coupled to asupport structure, such as a cantilever, which is in turn coupled to asubstrate. The support structure includes the conductive lead and thepiezoresistive material. In another example, the piezoresistive materialis located proximate the target, such as above or below the target.

The present disclosure also provides a method of forming a target havinga conductive lead or a piezoresistive material. In one example, themethod forms a target having both a conductive lead and a piezoresistivematerial. In a particular implementation, the method includes forming asupport structure coupling a target to a substrate. In one example, aconductive material is deposited on the support structure. In anotherexample, a piezoresistive material is deposited on the supportstructure. In yet another example, a piezoresistive material and aconducting material are deposited on the support structure. In otherexamples, the conducting material is formed by doping silicon, such assilicon above or below the target, in the support structure, or in thesubstrate. In a further example, the piezoresistive material is formedby doping silicon, such as silicon above or below the target or in asupport structure.

In another embodiment, the present disclosure provides a method of usinga target having a conductive lead and a piezoresistive material. In oneimplementation, the method involves applying a current to the conductivelead to heat the piezoresistive material. The target is then irradiated.In a particular example, the piezoresistive material is heated such thatthe support structure melts, such as immediately prior to the targetbeing irradiated. This method can, for example, result in a targetsuspended in free space at the moment it is irradiated.

In another implementation, a piezoresistive material proximate thetarget is used to place a charge proximate the target, such as justbefore the target is irradiated. In yet another implementation, thepiezoresistive material, or the conductive material, is used toinfluence the products of target irradiation, such as to at leastpartially contain generated electrons, which can enhance protonacceleration.

There are additional features and advantages of the subject matterdescribed herein. They will become apparent as this specificationproceeds.

In this regard, it is to be understood that this is a brief summary ofvarying aspects of the subject matter described herein. The variousfeatures described in this section and below for various embodiments maybe used in combination or separately. Any particular embodiment need notprovide all features noted above, nor solve all problems or address allissues in the prior art noted above.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are shown and described in connection with thefollowing drawings in which:

FIGS. 1A through 1G are cross sectional diagrams illustrating a processfor forming funnel cone molds and targets according to an embodiment ofthe present disclosure.

FIG. 2 is an illustration of a top plan view of a funnel cone targetaccording to an embodiment of the present disclosure.

FIG. 3 is a scanning electron microscope image of a funnel cone targetaccording to an embodiment of the present disclosure.

FIG. 4 is a scanning electron microscope image of a funnel cone targetaccording to an embodiment of the present disclosure.

FIG. 5 is a schematic diagram illustrating how a funnel cone targetaccording to an embodiment of the present disclosure may be used.

FIGS. 6A-6H are cross sectional diagrams illustrating a process forforming funnel cone molds and targets having an extended neck sectionaccording to an embodiment of the present disclosure.

FIG. 7 is an illustration of a top plan view of a funnel cone targethaving an extended neck according to an embodiment of the presentdisclosure.

FIG. 8 is a scanning electron microscope image of a funnel cone targethaving an extended neck according to an embodiment of the presentdisclosure.

FIG. 9 is a scanning electron microscope image of a funnel cone targethaving an extended neck according to an embodiment of the presentdisclosure.

FIGS. 10A-10I are cross sectional diagrams illustrating a process forforming molds and targets having a Gaussian-shaped cross sectionaccording to an embodiment of the present disclosure.

FIG. 11 is an illustration of a top plan view of a target having aGaussian-shaped cross section according to an embodiment of the presentdisclosure.

FIG. 12 is a graph of height versus radius for targets havingGaussian-shaped profiles that may be formed using the method of thepresent disclosure.

FIG. 13 is an optical microscope image of a target having aGaussian-shaped cross section according to an embodiment of the presentdisclosure.

FIGS. 14A-14I are cross sectional diagrams illustrating a process forforming molds and targets having a cup located at the end of acantilever.

FIG. 15 is an illustration of a top plan view of a target having a cuplocated at the end of a cantilever according to an embodiment of thepresent disclosure.

FIG. 16 is an illustrative mask layout for a photomask that may be usedin etching the front side of the wafer in the process of FIGS. 14Athrough 14I.

FIG. 17 is an illustrative mask layout for a photomask that may be usedin etching the front side of the wafer in the process of FIGS. 14Athrough 14I.

FIG. 18 is a scanning electron microscope image of a target having a cuplocated at the end of a cantilever produced according to an embodimentof the present disclosure.

FIG. 19 is a scanning electron microscope image of a target having a cuplocated at the end of a cantilever produced according to an embodimentof the present disclosure.

FIG. 20 is a scanning electron microscope image of a target having a cuplocated at the end of a cantilever produced according to an embodimentof the present disclosure.

FIG. 21 is a scanning electron microscope image of a target having a cuplocated at the end of a cantilever produced according to an embodimentof the present disclosure.

FIG. 22 is a scanning electron microscope image of a target having a cuplocated at the end of a cantilever produced according to an embodimentof the present disclosure.

FIG. 23 is an illustrative mask layout for a photomask that may be usedin etching the front side of the wafer in the process of FIGS. 14Athrough 14I to produce a doubly-spanned target.

FIG. 24 is a scanning electron microscope image of a target having a cuplocated at the end of two cantilevers produced according to anembodiment of the present disclosure.

FIGS. 25A-25L are cross sectional diagrams illustrating a process forforming molds and targets having embedded metal slugs located at the endof a cantilever.

FIG. 26 is an illustration of a top plan view of a target havingembedded metal slugs located at the end of a cantilever according to anembodiment of the present disclosure.

FIG. 27 is an illustration of a top plan view of a target havingembedded metal slugs located at the end of a cantilever according to anembodiment of the present disclosure.

FIG. 28 is an illustrative mask layout for a photomask that may be usedin etching the front side of the wafer in the process of FIGS. 25Athrough 25L.

FIG. 29 is a scanning electron microscope image of a target havingembedded metal slugs located at the end of a cantilever according to anembodiment of the present disclosure.

FIG. 30 is a scanning electron microscope image of a target havingembedded metal slugs located at the end of a cantilever according to anembodiment of the present disclosure.

FIG. 31 is a scanning electron microscope image of a target havingembedded metal slugs located at the end of a cantilever according to anembodiment of the present disclosure.

FIGS. 32A-32K are cross sectional diagrams illustrating a process forforming molds and targets having metal dots located on a metal foil.

FIG. 33 is an illustration of a top plan view of a metal foil targethaving square metal dots disposed thereon according to an embodiment ofthe present disclosure.

FIG. 34 is an illustration of a top plan view of a metal foil targethaving circular metal dots disposed thereon according to an embodimentof the present disclosure.

FIGS. 35A-35I are cross sectional diagrams illustrating a process forforming molds and targets having a wedge shape.

FIG. 36 is an illustration of a top plan view of a metal foil targethaving a wedge shape according to an embodiment of the presentdisclosure.

FIGS. 37A-37M are cross sectional diagrams illustrating a process forforming stacked metal foil targets.

FIG. 38 is an illustration of a top plan view of a metal foil targethaving multiple metal layers according to an embodiment of the presentdisclosure.

FIG. 39 is a scanning electron microscope image of a target havingmultiple metal layers located at the end of a cantilever according to anembodiment of the present disclosure.

FIG. 40 is a scanning electron microscope image of a target havingmultiple metal layers located at the end of a cantilever according to anembodiment of the present disclosure.

FIG. 41 is a scanning electron microscope image of a target havingmultiple metal layers located at the end of a cantilever according to anembodiment of the present disclosure.

FIGS. 42A-42I are cross sectional diagrams illustrating a process forforming a target or mold formed in the shape of a Winston collector andhaving a hemisphere at the apex.

FIG. 43 is an illustration of a top plan view of a target or mold formedin the shape of a Winston collector and having a hemisphere at the apexaccording to an embodiment of the present disclosure.

FIGS. 44A-44J are cross sectional diagrams illustrating a process forforming a target or mold formed in the shape of a Winston collector andhaving an aperture at the apex.

FIG. 45 is an illustration of a top plan view of a target or mold formedin the shape of a Winston collector and having an aperture at the apexaccording to an embodiment of the present disclosure.

FIGS. 46A-46C are cross sectional diagrams illustrating a process forforming a target mounting apparatus according to an aspect of thepresent disclosure.

FIG. 47 is an illustration of a top plan view of a target mountingapparatus according to an embodiment of the present disclosure.

FIGS. 48A-48J are schematic representations of target mounting apparatusaccording to an embodiment of the present disclosure.

FIG. 49 is a schematic illustration of a target manipulation apparatusaccording to an embodiment of the present disclosure.

FIG. 50 is a schematic illustration of a target coupled to apiezoresistive material and a conductive lead according to an embodimentof the present disclosure.

DETAILED DESCRIPTION

Unless otherwise explained, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which this disclosure belongs. In case of conflict,the present specification, including explanations of terms, willcontrol. The singular terms “a,” “an,” and “the” include pluralreferents unless context clearly indicates otherwise. Similarly, theword “or” is intended to include “and” unless the context clearlyindicates otherwise. The term “comprising” means “including;” hence,“comprising A or B” means including A or B, as well as A and B together.Although methods and materials similar or equivalent to those describedherein can be used in the practice or testing of the present disclosure,suitable methods and materials are described herein. The disclosedmaterials, methods, and examples are illustrative only and not intendedto be limiting. Additional information useful for practicing the subjectmatter of the present disclosure can be found in U.S. patent applicationSer. No. 12/066,479, incorporated by reference herein to the extent notinconsistent with the present disclosure.

Funnel Cone

Referring generally to FIGS. 1A through 1G, cross sectional diagramsshow the progressive processing for forming funnel cone targetsaccording to variations of a first aspect of the present disclosure.

Referring first to FIG. 1A, a silicon substrate 100, such as p-typesilicon having a <100> crystal orientation, is provided as a substrate.In a particular example, the silicon is double polished. Thermal silicondioxide layers 114, 116, such as about 4 μm layers, are deposited onboth sides 106, 108 of the substrate 100. Silicon nitride layers 120,122 such as 2 μm layers, are deposited on the thermal silicon dioxidelayers 114, 116. The silicon nitride layers 120, 122, in some examples,are deposited in a manner such that the layers 120, 122 havecomparatively low stress, such as using low pressure chemical vapordeposition. Standard photolithography exposure and developing techniquesare used to define a temporary mask 128 on the silicon nitride layer120.

In one example, about 1.6 μm of photoresist, such as Shipley 3612, isdeposited on the silicon nitride layer 120. In a particular example, thesubstrate 100 is primed with Hexamethyldisilazane (HMDS) before applyingthe photoresist. The substrate 100 is then soft baked at 90° C. The masklayer is then patterned using conventional photolithography techniques,such as by exposing the substrate 100 to the desired mask pattern for asuitable period of time, such as about 1.7 seconds. In some examples,the substrate 100 is developed using LDD26W (available from Shipley Co.)developer and a 110° C. postbake.

As shown in FIG. 1B, the silicon nitride layer 120 is etched usingstandard semiconductor processing techniques, such as using a RIE(reactive ion etch) dry etch for 4 minutes, to clear windows 134. In aparticular example, the etch rate is about 300 Å/m. In a particularexample, the RIE employs a mixture of SF₆ and O₂. In some cases, visualinspection can be used to verify that the dry etch has etched throughthe entire silicon nitride layer 120.

A wet etch, such as 6:1 BOE, can be used to etch through the silicondioxide layer 114 on the windows 134. Remaining photoresist can bestripped by a suitable process, such as a standard O₂ etch. FIG. 1Bshows the structure resulting after these processing steps have beenperformed.

Using analogous masking and etch techniques to those described above, alarger window 140 is opened on the back side of the substrate 100. FIG.1C shows the structure resulting from these steps, including a masklayer 146 on the back side of the substrate 100. The mask layer 146 maybe removed as described above.

A standard pre-diffusion cleaning process is typically used prior tofurther processing of the substrate 100. A deep isotropic etch is usedto produce a central cone 152 capped with top 158 of silicon dioxide andsilicon nitride from layers 114, 120. The etch is typically stoppedbefore the top 158 falls off the cone 152. In a specific example, thedeep isotropic etch is performed using an STS Deep Reactive Ion SiliconEtcher (STS plc, Newport, UK), eliminating the standard sidewallpassivation step typically used in the Bosch process. The resultingstructure is shown in FIG. 1D.

The top 158 is removed to produce the structure shown in FIG. 1E. In oneimplementation, the top 158 is removed by soaking the substrate in 6:1BOE to etch the top 158.

A desired metal is then deposited on the front side of the substrate 100to form a metal layer 164. In a specific example, the metal layer isabout 10 μm of gold deposited by sputtering. The coated structure isshown in FIG. 1F.

Finally, the back side of the substrate 100 is removed using a standardKOH etch. The KOH removes the silicon from the substrate 100, leavingonly the metal layer 164 and support structures 170 where the back sideof the substrate 100 was still coated with silicon dioxide layer 116 andsilicon nitride layer 122.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, or less than about 5 μm. In aspecific example, the metal layer has a thickness of about 10 μm. Theheight of the targets is, in some examples, between about 50 μm andabout 500 μm, such as between about 100 μm and about 250 μm or betweenabout 150 μm and about 300 μm. The width of the neck of the targets is,in some examples, between about 1 μm and about 100 μm, such as betweenabout 5 μm and about 75 μm or between about 5 μm and about 50 μm.

A cross section of the foil target produced using the above-describedprocess is shown in FIG. 2. SEM images of targets formed from thisprocess are shown in FIGS. 3 and 4.

FIG. 5 presents a schematic illustration of a method of using a funnelcone target 206. An ignition laser, such as a high-energy short-pulseignition laser 210, is directed through the wide base 214 of the target206. Radiation from the ignition laser 210 is focused towards the neck218 of the target 206. Implosion lasers 222 are focused at fuel locatedproximate the tip of the target 206.

The funnel cone targets may be useful, as the long neck design cancreate magnetic fields at the neck base when irradiated, trapping energyat the tip of the target. This effect may give rise to hotter targetscompared with other target shapes. Adjusting the length of the neck caninfluence where the trapped energy is focused. These hot targets can beused, for example, in fast ignition laser fusion, such as to ignite afuel source.

Extended Neck Funnel Cone

Referring generally to FIGS. 6A through 6H, cross sectional diagramsshow the progressive processing for forming extended neck funnel conetargets according to variations of an embodiment of the presentdisclosure.

Referring first to FIG. 6A, a silicon substrate 300, such as p-typesilicon having a <100> crystal orientation, is provided as a substrate.In a particular example, the silicon is double polished. Thermal silicondioxide layers 314, 316, such as about 4 μm layers, are deposited onboth sides 306, 308 of the substrate 300. Silicon nitride layers 320,322 such as 2 μm layers, are deposited on the thermal silicon dioxidelayers 314, 316. The silicon nitride layers 320, 322, in some examples,are deposited in a manner such that the layers 320, 322 havecomparatively low stress, such as using low pressure chemical vapordeposition. Standard photolithography exposure and developing techniquesare used to define a temporary mask 328 on the silicon nitride layer320.

In one example, about 1.6 μm of photoresist, such as Shipley 3612, isdeposited on the silicon nitride layer 320. In a particular example, thesubstrate 300 is primed with Hexamethyldisilazane (HMDS) before applyingthe photoresist. The substrate 300 is then soft baked at 90° C. The masklayer is then patterned using conventional photolithography techniques,such as by exposing the substrate 300 to the desired mask pattern for asuitable period of time, such as about 1.7 seconds. In some examples,the substrate 300 is developed using LDD26W (available from Shipley Co.)developer and a 110° C. postbake.

As shown in FIG. 6B, the silicon nitride layer 320 is etched usingstandard semiconductor processing techniques, such as using a RIE(reactive ion etch) dry etch for 4 minutes, to clear windows 334. In aparticular example, the etch rate is about 300 Å/m. In a particularexample, the RIE employs a mixture of SF₆ and O₂. In some cases, visualinspection can be used to verify that the dry etch has etched throughthe entire silicon nitride layer 320.

A wet etch, such as 6:1 BOE, can be used to etch through the silicondioxide layer 314 on the windows 334. Remaining photoresist can bestripped by a suitable process, such as a standard O₂ etch. FIG. 6Bshows the structure resulting after these processing steps have beenperformed.

Using analogous masking and etch techniques to those described above, alarger window 340 is opened on the back side of the substrate 300. FIG.6C shows the structure resulting from these steps, including a masklayer 346 on the back side of the substrate 300. The mask layer 346 maybe removed as described above.

A standard pre-diffusion cleaning process is then typically performed onthe substrate 300. With reference to FIG. 6D, the substrate underlyingthe windows 334 is removed, such as using a dry etch. In a particularexample, the dry etch is performed using an STS Deep Reactive IonSilicon Etcher. However, the sidewall passivation step of the standardBosch process is typically eliminated. The etch is discontinued beforethe silicon nitride/silicon dioxide “top” 352 falls off the cone 358formed by the etching process.

The portions 364 extending outwardly from the tip 370 of the cone 358can be removed to produce the structure shown in FIG. 6E. This may beaccomplished, for example, by soaking the substrate 300 in a suitableetchant, such as 6:1 BOE. Because the front and back sides of theportions 364 are exposed to the etchant, they will etch twice as fast asthe portion of the top 352 over the tip 370 of the cone 358.

The neck of the cone 358 can be extended to produce the structure shownin FIG. 6F. In one example, the remaining silicon dioxide top 352 overthe cone tip 370 is used to protect the cone 358 while an etch, such asa dry anisotropic etch using an STS DRIE plasma etcher, is performed.The etch is continued until the neck of the cone 358 has the desiredshape.

With reference to FIG. 6G, a metal layer 376 may be deposited on thefront side 306 of the substrate 300. In one example, the metal layer 376is sputter coated onto the substrate 300. The metal layer 376 is, in aspecific example, a 10 μm layer of gold.

The substrate 300 over the window 340 may be removed using a suitableetch to produce the final target, shown in FIG. 6H. In a specificexample, KOH is used as the etchant.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, or less than about 5 μm. In aspecific example, the metal layer has a thickness of about 10 μm. Theheight of the targets is, in some examples, between about 50 μm andabout 500 μm, such as between about 100 μm and about 250 μm or betweenabout 150 μm and about 300 μm. The width of the neck of the targets is,in some examples, between about 1 μm and about 100 μm, such as betweenabout 5 μm and about 75 μm or between about 5 μm and about 50 μm.

FIG. 7 is a top plan view of a target formed by the above describedprocess. FIGS. 8 and 9 are SEM images of extended neck funnel conetargets produced using this process.

Gaussian Curved Targets

Certain embodiments of the present disclosure provide laser targetshaving cross sections resembling a Gaussian curve. The followingdiscussion provides an example of how such targets may be fabricated.Referring first to FIG. 10A, a silicon substrate 400, such as p-typesilicon having a <100> crystal orientation, is provided as a substrate.In a particular example, the silicon is double polished. Thermal silicondioxide layers 414, 416, such as about 4 μm layers, are deposited onboth sides 406, 408 of the substrate 400. Silicon nitride layers 420,422 such as 2 μm layers, are deposited on the thermal silicon dioxidelayers 414, 416. The silicon nitride layers 420, 422, in some examples,are deposited in a manner such that the layers 420, 422 havecomparatively low stress, such as using low pressure chemical vapordeposition. Standard photolithography exposure and developing techniquesare used to define a temporary mask 428 on the silicon nitride layer420.

In one example, about 1.6 μm of photoresist, such as Shipley 3612, isdeposited on the silicon nitride layer 420. In a particular example, thesubstrate 400 is primed with Hexamethyldisilazane (HMDS) before applyingthe photoresist. The substrate 400 is then soft baked at 90° C. The masklayer is then patterned using conventional photolithography techniques,such as by exposing the substrate 400 to the desired mask pattern for asuitable period of time, such as about 1.7 seconds. In some examples,the substrate 400 is developed using LDD26W (available from Shipley Co.)developer and a 210° C. postbake. The masking process produces thestructure shown in FIG. 10B, having windows 434 formed in the mask layer428.

Using analogous masking and etch techniques to those described above, alarger window 440 is opened on the back side of the substrate 400, asshown in FIG. 10B. The mask layer 446 may be removed as described above.

The windows 434 formed through the mask are etched, such as using a deepreactive-ion etch using the Bosch process. An STS plasma etcher may beused for this technique. The etch results in the structure shown in FIG.10C, having silicon pillars 452.

The silicon pillars 452 are rounded using an HNA wet etch. HNA is amixture of nitric acid, hydrofluoric acid, and acetic acid. Nitric acidoxidizes the silicon, which is then removed by hydrofluoric acid. Aceticacid acts a diluent. Water can also be used as a diluent, but aceticacid has the advantage of reducing dissociation of nitric acid. Varyingthe time and composition of the etch can be used to produce differentlyshaped targets. In a specific example, the HNA mixture includes about30% HF (49.23%), about 30% acetic acid, and about 40% nitric acid(69.51%). The structure resulting from the HNA etch is shown in FIG.10D. FIG. 10E shows the structure which results when the etch time isincreased. The height of the central pillar 448 has been reduced, inaddition to being rounded.

In a modified version of the above-procedure, after achieving thestructure shown in FIG. 10B, a deep reactive-ion etch, such as using anSTS DRIE plasma etcher, is used to produce the structure shown in FIG.10F, having silicon pillars 458. This structure can be achieved bylimiting the time the sidewalls of the etch trench are passivated duringthe Bosch process. This provides a more isotropic etch profile. A wetetch, such as 6:1 BOE, is used to remove the silicon dioxide layer 414.

A HNA etch, as described above, is used to round the silicon pillars 458and produce the structure shown in FIG. 10G. The HNA etch time cangreatly affect the curve of the pillars 458. Thus, in one example, shortwet etch intervals are used. The shape of the pillars 458 can beobserved between etches to gauge the progress of the etch so it can bestopped when the desired shape has been achieved.

The front of the silicon mold of FIG. 10D, 10E, or 10G is then coatedwith a metal layer 464, such as 10 μm of sputtered gold. The remainingsilicon substrate above the window 440 can then be removed using asuitable etch, such as a KOH wet etch, leaving a hollow target having across section in the shape of a Gaussian curve.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, or less than about 5 μm. In aspecific example, the metal layer has a thickness of about 10 μm. Theheight of the targets is, in some examples, between about 50 μm andabout 500 μm, such as between about 100 μm and about 250 μm or betweenabout 150 μm and about 300 μm. In other examples, the target height isless than about 200 μm, such as less than 150 μm, less than about 100μm, or less than about 50 μm.

A cross sectional view of the target created using the above-describedprocess is shown in FIG. 11. FIG. 12 is a graph of height (microns)versus radius (microns) for various Gaussian targets according thepresent embodiment. FIG. 13 is an optical microscope image of a targetformed using the disclosed technique.

Support Arm Target With End Cup

In some embodiments, it may be useful to have a target attached to acomparatively small amount of surrounding material. Doing so can, forexample, reduce electronic coupling between the target and thesurrounding environment, which can produce cleaner target ignition andmore radiation. Thus, the present disclosure provides targets attachedto a support arm, the support arm being coupled to a larger substrate.Although the following example describes a cup-shaped target, othertarget shapes can be formed at the end of the support arm. In addition,the cup target can be created without a support arm.

Referring first to FIG. 14A, a silicon substrate 500, such as p-typesilicon having a <100> crystal orientation, is provided as a substrate.In a particular example, the silicon is double polished. Thermal silicondioxide layers 514, 516, such as about 4 μm layers, are deposited onboth sides 506, 508 of the substrate 500. Silicon nitride layers 520,522 such as 2 μm layers, are deposited on the thermal silicon dioxidelayers 514, 516. The silicon nitride layers 520, 522, in some examples,are deposited in a manner such that the layers 520, 522 havecomparatively low stress, such as using low pressure chemical vapordeposition. Standard photolithography exposure and developing techniquesare used to define a temporary mask 528 on the silicon nitride layer520.

In one example, about 1.6 μm of photoresist, such as Shipley 3612, isdeposited on the silicon nitride layer 520. In a particular example, thesubstrate 500 is primed with Hexamethyldisilazane (HMDS) before applyingthe photoresist. The substrate 500 is then soft baked at 90° C. The masklayer is then patterned using conventional photolithography techniques,such as by exposing the substrate 500 to the desired mask pattern for asuitable period of time, such as about 1.7 seconds. In some examples,the substrate 500 is developed using LDD26W (available from Shipley Co.)developer and a 210° C. postbake. The masking process produces thestructure shown in FIG. 14B, having windows 534 formed in the mask layer528.

Using analogous masking and etch techniques to those described above,two windows 540 are opened on the back side of the substrate 500, asshown in FIG. 14C. The mask layer 528 may be removed as described above.

As shown in FIG. 14D, a thick resist layer 546 is deposited over thefront side of the substrate 500. The resist layer 546 is patterned toopen a central window 552. The window 552 leaves open a portion 558 ofthe silicon dioxide layer and silicon nitride layers intermediate thewindows 534. The central window 552 defines the diameter of the cup.

The exposed window 552 is then etched, such as using a dry etch. In aparticular example, the window 552 is etched using the DRIE Boschprocess. The etch continues until the cup has the desired depth. Theresulting structure is shown in FIG. 14E, where the substrate 500includes a circular void 564 having a ring 570 of silicon dioxide and aring 576 of silicon nitride around the top.

Typically, the substrate 500 is then cleaned. As shown in FIG. 14F, adesired metal layer 582 is then deposited on the front side of thesubstrate. In a specific example, the metal layer 582 is about 10 μm ofsputtered gold.

A photoresist layer 588 is then patterned in the form of a circular plugto cover the top and perimeter of the cup 594, as shown in FIG. 14G. Insome cases, multiple photoresist applications may be needed to provideadequate photoresist coverage.

When the photoresist layer 588 has been formed, the uncovered metallayer 582 is etched. In one example, the etchant is AU-5. Typically, thesubstrate 500 is then cleaned. The resulting structure is shown in FIG.14H. A top view of the structure is shown in FIG. 15.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, or less than about 5 μm. In aspecific example, the metal layer has a thickness of about 10 μm. Theheight of the targets is, in some examples, between about 5 μm and about500 μm, such as between about 10 μm and about 250 μm or between about 10μm and about 100 μm. In other examples, the target height is less thanabout 150 μm, such as less than 100 μm, less than about 50 μm, or lessthan about 15 μm. The diameter of the cup portion of the target is, insome examples, between about 10 μm and about 500 μm, such as betweenabout 50 μm and about 250 μm or between about 75 μm and about 150 μm. Ina specific example, the cup diameter is about 100 μm.

FIGS. 16 and 17 are top level masks of the die shape etched into thesilicon nitride layer 520. FIGS. 18-22 are SEM images of a cup targetcoupled to a cantilever formed using the above-described process.

FIG. 23 illustrates an alternative mask that can be used in theabove-described process. The mask includes a cantilever shape coupled toa handling die. A target, such as a cup shaped target, is coupled to thecantilever using spans. This doubly spanned target produced by the maskcan have various advantages. For example, the target may be less likelyto move, as it is supported on both sides. Although FIG. 19 illustratesa doubly spanned target, similar masks can be created to produce targetshaving other numbers of spans, such as targets having three or fourspans. FIG. 24 is an SEM image of a target produced using the mask ofFIG. 23.

The cup shaped target may have advantages over other target shapes. Forexample, it may prevent the pre-pulse of a laser from travelling aroundthe target and forming a dense plasma wall on the target's backside.Such a plasma can interrupt the projection of the ion/proton/electronemission from the target. The cup can provide a comparativelyuninhibited backside surface.

The mounting arm or cantilever can also have advantages. For example, itmay provide a more effective and efficient mounting system for thetargets, as well as generally greater ease in handling the targets. Inaddition, the reduced mass of the mount can minimize energy fromescaping into the target holder. Thus, more energy input into the systemcan be focused on the target itself. Other target and mold shapes andtheir methods of production, including those discussed in the presentdisclosure, can be adapted to include the mounting arm.

Support Arm Target With Metal Slugs

In another aspect, rather than a cup, a support structure, such as acantilever, is used to support a target having embedded metal slugs.However, the metal slug targets may also be formed without a supportstructure.

As shown in FIG. 25A, silicon nitride layers 614, 616, such as a 2 μmthick layers, are deposited on the front side 606 and back side 608 of asubstrate 600, such as <100> p-type silicon. In a particular example,the silicon is double polished. In a specific implementation, thesilicon nitride layers 614, 616 have comparatively low stress, which maybe achieved, for example, using low pressure chemical vapor deposition.The silicon nitride layer 614 is coated with photoresist and exposed toform two windows 628 in the photoresist layer 622.

A dry etch, such as a dry reactive-ion etch, for example using the Boschprocess, is used to remove the silicon nitride layer 614 underneath thewindows 628.

With reference to FIG. 25B, the back side 608 of the substrate 600 iscoated with photoresist and exposed to form a window 640 in thephotoresist layer 634. A dry etch, such as a dry reactive-ion etch, isused to etch the silicon nitride layer 616 and substrate 600 underneaththe window 640. In a particular example, the etch employs SF₆ and O₂.The etch is continued until the void 646 reaches the silicon nitridelayer 614 over the front side 606 of the substrate 600.

Turning now to FIG. 25C, a metal layer 652, such as a 0.5 μm layer ofchromium, is deposited on the front side 606 of the substrate 600. In aparticular example, the metal layer 652 is deposited by sputter coating.

The substrate 600 is prepared for a standard metal life-off process. Asshown in FIG. 25D, a thick photoresist layer 658 is deposited over themetal layer 652. The resist layer 658 is patterned with a desiredfeature, such as a window 664 into which a metal slug may be deposited.After developing the window 664, a metal layer 670, such as a 5 μm layerof copper, is deposited over the resist layer 658 and window 664. In oneexample, the metal layer 670 is deposited by evaporation. Although FIG.25D shows a single metal layer 670, multiple metal layers may bedeposited, if desired. In a more specific example, a standard metallift-off is performed after each metal layer is deposited.

Although FIG. 25D illustrates a single window 664 where a dot or slugmay be deposited, other metal patterns can be formed. For example, FIG.25E illustrates a substrate having two metal dots 676. When the dots 676are of the same material, they can be formed as described for FIG. 25D,except two windows are used rather than the single window 664. Whendifferent materials are desired for the dots 676, a first dot can bedeposited as described for FIG. 25D. The process can then be repeatedusing a different mask forming a new window into which the secondmaterial can be deposited and, optionally, covering the first dot.

Continuing from FIG. 25D, the lift-off may be performed, in one example,by removing the portions of the metal layer 670 over the resist layer658 by washing the substrate 600 in a sonicated acetone bath, producingthe structure shown in FIG. 25F.

Typically, a standard wafer cleaning process is then performed on thesubstrate 600. If another metal is desired in the final target, it canthen be added to the substrate 600. In one example, the substrate 600 iscoated, such as by sputter coating, with another metal layer 682, suchas a 5 μm aluminum layer, as shown in FIG. 25G. Standardphotolithography techniques are used to deposit and pattern a resistlayer 688, which is used to protect the portion of the metal layer 682desired in the final target. The portion of the metal layer 682 notcovered by resist 688 is removed, such as with a wet etch. In aparticular example, PAD (available from Ashland Specialty Chemicals, ofDublin, Ohio) is used as the etchant, producing the structure shown inFIG. 25H.

A standard wafer cleaning process is then typically performed on thesubstrate 600. As shown in FIG. 25I, a protective metal layer 694, suchas a 0.5 μm gold layer, is deposited on the front side of the substrate600. The metal layer 694 protects the metal layer 682 while silicon inthe substrate 600 is removed, such as using a KOH wet etch. KOH willetch aluminum, but not gold.

In order to remove the silicon from the substrate 600, standardphotolithography techniques are used to pattern a window 698, shown inFIG. 25J, in the silicon nitride layer 616. A dry etch, such as dryreactive-ion etch, can be used to remove the silicon nitride layer 616under the window 698. The silicon under the window 698 is then removed,such as using a wet etch, for example with a KOH etchant. The resultingstructure is shown in FIG. 25K. The substrate 600 is then carefullyrinsed. The resulting material is typically fragile, and so carefulhandling can be beneficial. For example, side to side translation of thesubstrate 600 can cause the target to become damaged.

The protective metal layer 694 can then be removed, producing thestructure shown in FIG. 25L. When the protective layer 694 is a goldlayer, it can be removed using a wet gold etch, such as using Au-5 asthe etchant, as it typically will not etch other metals, such asaluminum or chromium.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, less than about 5 μm, or less thanabout 2 μm. In further example, the metal layer thickness is betweenabout 1 μm and about 50 μm, such as between about 2 μm and about 20 μm.In a specific example, the metal layer has a thickness of about 10 μm.The diameter of the target is, in some examples, between about 10 μm andabout 500 μm, such as between about 50 μm and about 250 μm or betweenabout 75 μm and about 150 μm. In a specific example, the target diameteris about 25 μm. In further examples, the target diameter is less thanabout 50 μm, such as less than about 25 μm, or less than about 10 μm.

FIG. 26 is a cross sectional view of a target formed using theabove-described process and having a single metal-containing dot. FIG.27 is a cross sectional view of a target formed using theabove-described process and having two metal containing dots. FIG. 28 isan image of a mask useable in the above-described process.

FIGS. 29-30 are SEM images of a target formed using the above-describedprocess and having a single metal-containing dot. FIG. 31 is an SEMimage of a target formed using a variation of the above-describedprocedure having a bowl-like structure. This structure can be producedby the above-described method, but omitting the silicon dioxide layerfrom the front side of the substrate. The silicon nitride etchingprocess will also etch the underlying silicon to a degree, creating avoid over which the metals can then be deposited. Thus, the silicondioxide layer as a protective layer for the substrate during siliconnitride layer etching.

Dotted Metal Foil

In some embodiments, it may be useful to have a target formed from ametal foil and having metal dots disposed on a surface of the foil. Asshown in FIG. 32A, silicon dioxide layers 714, 716, such as 4 μm layers,are deposited on the front 706 and back 708 sides of a substrate 700,such as <100> p-type silicon. In a particular example, the silicon isdouble polished. Silicon nitride layers 722, 724, such as 2 μm thicklayers, are then deposited on the silicon dioxide layers 714, 716. Thesilicon nitride layers 722, 724 are typically deposited so that theyhave comparatively low stress, such as using low pressure chemical vapordeposition.

As shown in FIG. 32B, a photoresist layer 730 is deposited on thesilicon nitride layer 722 and patterned to form three windows 736. A dryetch, such as dry reactive-ion etch, is used to remove the siliconnitride layer 722 under the windows 736. The dry etch process can bemonitored visually.

A photoresist layer 742 is deposited on the silicon nitride layer 724and patterned to form a window 748. The silicon nitride layer 724beneath the window 748 is etched, such as using a dry etch, for examplea dry reactive-ion etch. The silicon dioxide layer 716 under the window748 is then etched, such as using a wet etch. In a specific example, thewet etch is performed using a 6:1 BOE etchant.

A metal layer 754 is deposited on the front side 706 of the substrate700, as shown in FIG. 32C. The metal layer 706 may be applied, in oneexample, by sputter coating, such as a 0.5 μm layer of gold.

With reference to FIG. 32D, a photoresist layer 760 is deposited on themetal layer 754 and exposed such that only the metal which is desired toremain after a subsequent etch step is coated with the photoresist layer760.

A metal etch, such as a wet metal etch, is used to remove the portion ofthe metal layer 754 not covered by the photoresist layer 760, as shownin FIG. 32E. In one example, Au-5 is used as the etchant, as it canremove gold yet typically does not etch the photoresist.

A photoresist layer 766 is then applied to the front side 706 of thesubstrate 700 in preparation for a standard metal lift-off step.Typically the substrate 700 is cleaned prior to depositing thephotoresist layer 766. The photoresist layer 766 is then patterned asdesired, such as using a glass plate mask, to produce desired featuresof interest 772, as shown in FIG. 32G. In one example, the features ofinterest 772 are a pattern or array of shapes, such as circles orsquares.

With reference to FIG. 32H, a metal layer 778 is deposited on the frontside 706 of the substrate 700, such as by evaporation. In one example,the metal layer 778 is about 1 μm of copper.

The metal lift-off process is completed, in one example, by soaking thesubstrate 700 in a sonicated acetone bath. Portions of the metal layer778 located over photoresist 766 will be removed, as shown in FIG. 32I.In the case of the specifically described example, an array of copperdots is located on a gold metal foil.

FIG. 32J illustrates the substrate 700 after silicon has been removed,such as by performing a wet etch. In a specific example, the etchant isKOH. This step produces a freestanding metal film located on a silicondioxide/silicon nitride spatula.

The substrate 700 is typically rinsed and cleaned. The silicon dioxidelayer 714 can be removed using a suitable etch, such as a wet etch using6:1 BOE. As shown in FIG. 32K, this step produces a bilayer metal foilthat is spanned on a silicon nitride four-pronged spatula having an openwindow in the center, which can reduce interference with a laser.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, less than about 5 μm, or less thanabout 2 μm. In further example, the metal layer thickness is betweenabout 1 μm and about 50 μm, such as between about 2 μm and about 20 μm.In a specific example, the metal layer has a thickness of about 10 μm.In some examples, the dots have a diameter of less than about 25 μm,such as less than about 10 μm, less than about 5 μm, less than about 2μm, or less than about 1 μm. The thickness of the dots is, in someexamples, between about 10 nm and about 5000 nm, such as between about100 nm and about 1000 nm or between about 250 nm and about 750 nm. In aspecific example, the thickness of the dots is about 500 nm. In furtherexamples, the spacing between dots is between about 25 μm and about 500μm, such as between about 50 μm and about 250 μm. In a particularexample, the spacing between dots is about 100 μm.

FIG. 33 is a top view of a foil dotted with squares produced accordingto the above-described method. FIG. 34 is a top view of a foil dottedwith circles produced according to the above-described method.

Metal Foil Wedge Targets

Another embodiment of the present disclosure provides wedge-shaped metalfoil targets. A process for producing such targets is illustrated inFIGS. 35A-35I. As illustrated in FIG. 35A, front 806 and back 808 sidesof a substrate 800, such as <100> p-type silicon, are coated withsilicon nitride layers 812, 814. In a particular example, the silicon isdouble polished. In at least some examples, the silicon nitride layers812, 814 are deposited so that they have comparatively low stress, suchas by low pressure chemical vapor deposition. In a specific example, thesilicon nitride layers 812, 814 have a thickness of about 2 μm.

A photoresist layer 818 is deposited on the silicon nitride layer 812,patterned, and developed to open two windows 822. The silicon nitridelayer 812 under the windows 822 is then etched, such as using a dryetch.

With reference to FIG. 35B, a photoresist layer 826 is deposited on thefront side 806 of the substrate. The photoresist layer 826 is thenpatterned and developed to open a window 830 between the windows 822.

A metal layer 834 is deposited on the front side 806 of the substrate800, as shown in FIG. 35C. In some implementations, the metal isdeposited by evaporation. The metal layer 834, in a specific example, isa 10 μm layer of aluminum.

A standard lift off procedure is used to remove portions of the metallayer 834 overlying the photoresist layer 826. For example, thesubstrate 800 may be placed in a sonicated acetone bath. The resultingstructure is shown in FIG. 35D.

With reference to FIG. 35E, a photoresist layer 838 is deposited on thesilicon nitride layer 814 on the back side 808 of the substrate 800. Thephotoresist layer 838 is patterned and developed to open windows 842corresponding to windows 822 and 830. The silicon nitride layer 814 anda portion of the substrate 800 under the windows 842 is removed using asuitable etch. In one example, the etch is a deep silicon anisotropicetch.

The front side 806 is mechanically ground, such as using a die, toproduce a metal layer 834 having a desired angle, as shown in FIG. 35F.The die is typically positioned at the center of the substrate 800 inorder to improve the accuracy and symmetry of the grinding process.

With reference to FIG. 35G, when the metal layer 834 may be etchedduring subsequent steps, it may be desirable to deposit a protectivemetal layer 846 over the metal layer 834. In one example, the protectivemetal layer 846 is deposited by sputter coating the front side 806 ofthe substrate 800. The protective metal layer 846 may be a gold layer,such as a 0.5 μm thick gold layer.

An etch, such as a wet etch, is then used to remove remaining substrate800 under the windows 842. In a specific example, KOH is used as theetchant. The etch results in the structure shown in FIG. 35H.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, less than about 5 μm, or less thanabout 2 μm. In further example, the metal layer thickness is betweenabout 1 μm and about 50 μm, such as between about 2 μm and about 20 μm.In a specific example, the metal layer has a thickness of about 10 μm.

The protective metal layer 846 may then be removed to produce thestructure shown in FIG. 35I, such as using a suitable etching process.When the protective metal layer 846 is a gold layer, it may be removedusing an Au-5 wet etch.

A top view of a target formed according to the present disclosure isshown in FIG. 36.

Stacked Metal Foils

Another embodiment of the present disclosure provides a stacked metalfoil target and a method for their fabrication. The fabrication processis summarized in FIGS. 37A-37M.

With reference first to FIG. 37A, the front 906 and back 908 sides of asubstrate 900, such as <100> p-type silicon, are coated to form siliconnitride layers 912, 914. In a particular example, the silicon is doublepolished. In some examples, the silicon nitride layers 912, 914 aredeposited in a manner such that they have comparatively low stress, suchas using low pressure chemical vapor deposition. A photoresist layer 918is deposited over the silicon nitride layer 912. The photoresist layer918 is then patterned and developed to open a central window 922.

One or more metal layers are deposited in the window 922. The followingdiscussion provides an example of a process for producing a specifictarget. However, this process can be varied depending on the number ofmetal layers desired, types of metal layers desired, and order ofmetals.

With reference to FIG. 37B, a first metal layer 926, such as a 100 nmlayer of aluminum, is deposited in the window 922. In a particularexample, the aluminum is deposited by evaporation. A second metal layer930, such as 1 μm of copper, is deposited over the first metal layer,such as by evaporation, as shown in FIG. 37C. This process is repeatedfor additional layers, such as a 50 nm layer of titanium 932 (FIG. 37D),a 6 μm layer of copper 934 (FIG. 37E), a 50 nm vanadium layer 936 (FIG.37F), and a 6 μm copper layer 938 (FIG. 37G).

Once the desired metal layers have been deposited, unwanted metalportions located above the photoresist layer 918 can be removed using astandard lift off technique to produce the structure shown in FIG. 37H.In a specific implementation, the substrate 900 is sonicated in anacetone bath. A protective metal layer 942, shown in FIG. 37I, isdeposited over the upper metal layer 938, in some examples, to protectthe metal layers during further processing of the substrate 900. In oneexample, the protective metal layer 942 is deposited by sputter coating.The protective metal layer 942 is, in one example, a 0.5 μm gold layer.

With reference now to FIG. 37J, a photoresist layer 946 is deposited onthe back side 908 of the substrate 900, patterned, and developed toexpose windows 950. The silicon nitride layer 914 and substrate 900under the windows 950 are etched using suitable techniques, such as asilicon nitride dry etches followed by a deep anisotropic silicon etch.Remaining substrate 900 under the windows 950 is then removed using asuitable wet etch, such as using a KOH etchant, to produce the structureshown in FIG. 37K. The substrate 900 is typically cleaned after the wetetch.

As shown in FIG. 37L, a suitable etch, such as a dry silicon nitrideetch, is used to remove the exposed silicon nitride layers 912, 914.Finally, the protective metal layer 942 is removed to produce thestructure shown in FIG. 37M. When the protective metal layer 942 is agold layer, it may be removed using Au-5 as the etchant. The resultingtarget is a metal stack suspended over a hollow silicon die.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, less than about 5 μm, or less thanabout 2 μm. In further example, the metal layer thickness is betweenabout 1 μm and about 50 μm, such as between about 2 μm and about 20 μm.In a specific example, the metal layer has a thickness of about 10 μm.

FIG. 38 is a top view of a metal target formed using the above describedmethod. FIGS. 39-41 are SEM images of metal foil stack targets producedusing the above technique attached to a silicon nitride cantilever.

Winston Collector Having a Hemispherical Apex

A Winston collector target having a hemispherical apex is provided byanother aspect of the present disclosure. A process for manufacturingthe target is described in FIGS. 42A-42I. As shown in FIG. 42A, standardphotolithography techniques are used to deposit a photoresist layer 1012on the backside 1008 of a substrate 1000, such as <100> p-type silicon.In a particular example, the silicon is double polished. The photoresistlayer 1012 is patterned and developed to expose a window 1018.

With reference to FIG. 42B, an inverse hemisphere 1024 is opened underthe window 1018, such as using a dry etch, for example an isotropic drysilicon etch. The photoresist layer 1012 is removed and a siliconnitride layer 1030, such as a 1 μm thick layer, is deposited on the backside 1008 of the substrate 1000, as shown in FIG. 42C. In a particularexample, the entire substrate 1000 is coated with silicon nitride, suchas using low pressure chemical vapor deposition, and the silicon nitrideis removed from the front side 1006 of the substrate using a blanketetch-leaving only the silicon nitride layer 1030.

Turning to FIG. 42D, a silicon dioxide layer 1036, such as a 4 μm thickthermal silicon dioxide layer, is formed on the front side 1006 of thesubstrate 1000. Standard photolithography processes are used to deposita photoresist layer 1042 on the silicon dioxide layer 1036, as shown inFIG. 42E. The photoresist layer 1042 is patterned and developed to forma window 1048. The silicon dioxide layer 1036 under the window 1048 isetched using a suitable process, such as a using a dry silicon dioxideetch. In a specific example, the window 1048 is circular.

A deep isotropic etch is performed on the front side 1006 of thesubstrate 1000. FIG. 42F shows the results of this process, where acavity 1054 is formed under the window 1048. In a particular example,the deep isotropic etch is a Bosch process or a variant thereof. Forexample, eliminating the side-wall passivation step of the Bosch processcan produce a cavity 1054 having a Gaussian profile.

The front side 1006 of the substrate 1000 is then blanket etched toremove the silicon dioxide layer 1036, as shown in FIG. 42G. Withreference to FIG. 42H, a desired metal layer 1060 is then deposited onthe front side 1006 of the substrate 1000. In a particular example, themetal layer 1060 is deposited by sputter coating. The metal layer 1060is a 10 μm gold layer, in a specific example.

The silicon nitride layer 1030 and a portion of the substrate 1000thereunder are etched, such as using a wet etch. The etchant, in aparticular example, is KOH. In at least some implementations, the etchis timed to leave a portion of the substrate 1000 to act as a handlingdie. The final target is shown in FIG. 42I. A top view of the target isshown in FIG. 43.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, less than about 5 μm, or less thanabout 2 μm. In further example, the metal layer thickness is betweenabout 1 μm and about 50 μm, such as between about 2 μm and about 20 μm.In a specific example, the metal layer has a thickness of about 10 μm.The height of the targets is, in some examples, between about 50 μm andabout 500 μm, such as between about 100 μm and about 250 μm or betweenabout 150 μm and about 300 μm. In some examples, the full width at thehalf maximum height of the target is between about 10 μm and about 500μm, such as between about 15 μm and about 350 μm or between about 30 μmand about 300 μm.

The Winston collector with the hemisphere apex may be used, in someexamples, as a hohlraum. The hemisphere can focus incident laser energyto produce a hot spot away from the target.

Open Apex Winston Collector

A Winston collector target with an aperture at its apex is provided byanother aspect of the present disclosure. A process for producing thistarget is summarized in FIGS. 44A-44J. With reference first to FIG. 44A,silicon nitride layers 1112, 1114, such as 2 μm thick layers depositedby low pressure chemical vapor deposition, or another process thatproduces silicon nitride layers having relatively low stress, are formedon the front 1106 and back 1108 sides of a substrate 1100, such as <100>p-type silicon. In a particular example, the silicon is double polished.Standard photolithography techniques are used to deposit a photoresistlayer 1120 on the silicon nitride layer 1112. The photoresist layer 1120is patterned and developed to open a window 1126 in the photoresistlayer 1120.

The silicon nitride layer 1112 under the window 1126 is etched using asuitable process, such as a dry etch, to produce the structure shown inFIG. 44B. Visual inspection can be used to verify when the siliconnitride layer 1112 has been completely etched. Turning to FIG. 44C, acavity 1132 is opened under the window 1126 using a suitable etchingprocess. In a particular example, the etch is a deep isotropic dry etch,such as using the Bosch process. The Bosch process can be controlled tovary the shape of the cavity 1132. For example, eliminating the sidewallpassivation step can produce a cavity 1132 having a Gaussian-likeprofile.

The photoresist layer 1120 is removed and the back side 1108 of thesubstrate 1100 is coated with a photoresist layer 1138. The photoresistlayer 1138 is patterned and developed to produce a window 1144. Thesilicon nitride layer 1114 under the window 1144 is etched away, such asusing a dry etch, to produce the structure shown in FIG. 44D. As shownin FIG. 44E, the photoresist layer 1138 and the silicon nitride layer1112 are then removed. In a particular example, the silicon nitridelayer 1112 is removed using a blanket dry etch.

A desired metal layer 1150 is formed on the front side 1106 of thesubstrate, such as by sputter coating, producing the structure shown inFIG. 44F. In a particular example, the metal layer 1150 is a 10 μm layerof gold.

FIG. 44G illustrates the structure formed after the substrate 1100 underthe window 1144 has been etched. In a particular example, the etch is adry etch. The silicon nitride layer 1114 acts as a mask for this etchingprocess. Next, with reference to FIG. 44H, the metal layer 1150 over thewindow 1144 is etched away. This step may be performed using a wet ordry etch. When a wet etch is used, the entire substrate 1100 istypically not placed in the etchant. Rather, the etchant is contact withthe back side 1108 of the substrate 1100. Optical inspection, such aswith a microscope, can be used to verify that the etch is complete.

Typically, the substrate 1100 is then cleaned and the remaining siliconnitride layer 1114 is removed, such as using a blanket dry etch,producing the structure shown in FIG. 44I. Finally, as shown in FIG.44J, the back side 1108 of the substrate 1100 is etched. When the metallayer 1150 is a gold layer, KOH may be used as the etchant, as gold isimpervious to KOH. A top view of the target formed from this method isshown in FIG. 45.

In some example, the targets created using the above-describe processhave metal layer thickness of less than about 20 μm, such as less thanabout 15 μm, less than about 10 μm, less than about 5 μm, or less thanabout 2 μm. In further example, the metal layer thickness is betweenabout 1 μm and about 50 μm, such as between about 2 μm and about 20 μm.In a specific example, the metal layer has a thickness of about 10 μm.The height of the targets is, in some examples, between about 50 μm andabout 500 μm, such as between about 100 μm and about 250 μm or betweenabout 150 μm and about 300 μm. In some examples, the full width at thehalf maximum height of the target is between about 10 μm and about 500μm, such as between about 15 μm and about 350 μm or between about 30 μmand about 300 μm.

The Winston collector with the hemisphere apex may be used, in someexamples, as a hohlraum. The hemisphere can focus incident laser energyto produce a hot spot away from the target.

The Winston collector shape may be useful in focusing incident laserradiation to a desired point. The incident angles of the Winstoncollector are all tangent to the center of the apex. Thus, laseralignment with the target can be less of a concern.

Target Alignment System

In addition to targets, the present disclosure provides an apparatus foraligning targets. For example, the targets may be aligned such thatradiation hitting one target is directed to one or more other targets.In one example, the target alignment apparatus includes apertures formedin a substrate into which targets, such as targets attached to handlingdie, may be placed. The depth and orientation of the apertures may becontrolled to provide the desired target orientation. A process forproducing a target alignment apparatus is illustrated in FIGS. 46A-46C.

With reference first to FIG. 46A, silicon nitride layers 1212, 1214 areformed on the front 1206 and back 1208 sides of a substrate 1200, suchas <100> p-type silicon. In a particular example, the silicon is doublepolished. A photoresist layer 1220 is deposited on the silicon nitridelayer 1212 and patterned to open windows 1226. The silicon nitride layer1212 under the windows 1226 is then removed, such as using a dry etch.

The substrate 1200 underneath the windows 1226 is then removed toproduce the structure shown in FIG. 46B. In a specific example, thesubstrate 1200 is removed using a deep anisotropic silicon dry etch,such as the Bosch process. Finally, the photoresist layer 1220 isremoved, producing the structure shown in FIG. 45C.

Although three windows 1226 are illustrated in FIG. 46C, the targetapparatus may have more or fewer windows. In addition, the depth of thewindows 1226 may be controlled, such as by forming the windows 1226through multiple mask-etch cycles.

In examples, the target apparatus has dimensions of between about 1 mm×1mm×1 mm and about 50 mm×50 mm×50 mm, such as between about 2 mm×2 mm×3mm and about 10 mm×10 mm×12 mm. In a specific example, the targetapparatus has dimensions of about 4 mm×4 mm×5 mm.

FIG. 47 illustrates a top view of a target alignment system producibleusing the above-described process. FIGS. 48A-48J are various views ofdifferent types of targets and target alignment apparatus combinationsproducible using the above-described technique.

Target Wafer Handling System

Some embodiments of the present disclosure produce multiple targetslocated on a single substrate, such as a silicon wafer. One advantage ofthese multiple target wafers is that they can be mechanicallymanipulated, including in an automated manner. Mechanical manipulationcan be useful, for example, in aligning a target with the path of alaser. Mechanical manipulation may also allow multiple targets to berapidly and successively placed in a desired location, such as the pathof a laser. For example, the wafer is positioned to place a first targetin the path of a laser. The first target is irradiated by the laser. Thewafer is the positioned to place a second target in the path of thelaser. This process can be repeated as desired. The wafer may includetargets that are all of the same type or targets that are of differenttypes. When different types of targets are included in a single wafer,mechanical manipulation may be used to place a desired target type in adesired location, such as in the path of a laser.

In a particular example, a complete wafer of target die, spacedaccording to experimental or process needs, are held in a suitableholding device, such as an edge clipped wafer holder on a rotary platesuspended from an xyz-theta stage with an insulating holding rod. Therotary plate is rotated with a suitable actuator, such as a chain orbelt drive. A suitable rotary plate mechanism is disclosed in U.S. Pat.No. 6,217,034, incorporated by reference herein to the extent notinconsistent with the present disclosure. Typically the actuator is suchthat it is kept away from the laser target interaction area. Softwareand motors are used to control the location of targets on the rotaryplate via rotation of the plate and xyz-theta manipulation of the stage,in some examples. Suitable stages, and rotary mechanisms, are availablefrom Newmark Systems, Inc. of Mission Viejo, Calif. In other examples,the rotary plate or stage are manually controlled. This apparatus can beused, in some examples, to quickly align individual targets on a givenwafer between the laser and the subject of interest at slow or highrepetition rates and without the need to insert individual targets intoa support wafer, or insert individual targets and stalks in front of thelaser one or two at a time.

Targets Coupled to Piezoresistor or Conductive Leads

In another aspect of the present disclosure, targets are provided thatinclude a piezoresistor or conductive leads. The piezoresistor, in somecases, is coupled to the conductive leads. In one example, thepiezoresistive material is located proximate the target, such as aboveor below the target. In another example, the piezoresistive material islocated on a support structure, such as a cantilever coupling the targetto a substrate. The piezoresistive material or conductive material canbe deposited during target fabrication, in some examples.

In a particular method, target fabrication includes the step of forminga support structure that connects a target to a substrate. The supportstructure is a cantilever, in some examples. The support structure ismasked to form a pattern into which the piezoresistive material can bedeposited. The piezoresistive material is then deposited into thepattern. In another example, a surface of the substrate is coated withthe piezoresistive material, the desired portion of the piezoresistivematerial is masked, and unwanted piezoresistive material is removed,such as by etching. The support structure is masked to form a patterninto which the conductive material can be deposited. The conductivematerial, such as a conductive metal, is then deposited into thepattern.

In other examples, the conductive material is formed by doping silicon,such as silicon in a support structure or silicon proximate the target.For example, ion bombardment can be used to inject silicon atoms withnegative ions, using phosphorus doping, or positive ions, using borondoping. In further examples, the piezoresistive material is formed bymodifying the silicon, such as the silicon proximate a target or in asupport structure. In a specific example, the silicon modification isdoping the silicon, such as using ion bombardment.

Targets with conductive leads or piezoresistive sections can havevarious advantages. For example, when the leads or piezoresistivematerial is located in a support structure, current can be applied tothe support structure, such as immediately before a target isirradiated. The current causes the support structure to melt, leavingthe target suspended in space as it is irradiated. This can reduceinterference with the irradiation process or the products thereof. Inanother example, when the piezoresistive material is located proximatethe target, it can be used to apply a positive or negative charge to thetarget, such as immediately prior to target irradiation. In yet anotherexample, the piezoresistive material, or the conductive material, isused to influence the products of target irradiation, such as to atleast partially contain generated electrons, which can enhance protonacceleration.

The disclosed targets can provide a number of advantages. For example,the lithographic techniques used to produce the target may allow manytargets to be fabricated and fabricated with consistent properties.Accordingly, the present disclosure may allow targets to be constructedless expensively than using prior techniques. Because of the potentiallylower cost, or greater numbers of targets that can be made, such methodsmay allow the targets to be used in more applications, as well aspotentially increasing the quality or quantity of data available fromtarget experiments. In further implementations, the targets can befabricated with a surrounding support that can help protect the targetfrom damage and aid in handling and positioning the target.

It is to be understood that the above discussion provides a detaileddescription of various embodiments. The above descriptions will enablethose skilled in the art to make many departures from the particularexamples described above to provide apparatuses constructed inaccordance with the present disclosure. The embodiments areillustrative, and not intended to limit the scope of the presentdisclosure. The scope of the present disclosure is rather to bedetermined by the scope of the claims as issued and equivalents thereto.

What is claimed is:
 1. A structure for facilitating proton generation,the structure comprising: a handling die, the handling die containing anaperture; a destructible laser target located in the aperture, thedestructible laser target configured to emit protons upon irradiation; asupport structure for coupling the destructible laser target to thehandling die prior to irradiation of the destructible laser target; anda piezoresistive element; wherein the destructible laser target isconfigured to be decoupled from the handling die at a time ofirradiating the destructible laser target.
 2. The structure of claim 1,wherein the support structure laterally couples the destructible lasertarget to the handling die.
 3. The structure of claim 1, wherein atleast one of a depth of the aperture, a position of the aperture, and anorientation of the aperture is configured to control a relativealignment of the destructible laser target with a second destructiblelaser target.
 4. The structure of claim 1 comprising at least one othersupport structure for coupling the destructible laser target to thehandling die prior to irradiation of the destructible laser target. 5.The structure of claim 1, wherein the support structure is a cantilever.6. The structure of claim 5, wherein the support structure has across-section with a dimension less than 15 μm².
 7. The structure ofclaim 1, wherein the piezoresistive element is configured to facilitateapplication of an electric charge to the destructible laser target. 8.The structure of claim 7, further comprising a conductive lead coupledto a piezoresistive element.
 9. The structure of claim 7, furthercomprising a conductive lead configured to influence types of particlesemitted upon irradiation of the destructible laser target.
 10. Thestructure of claim 9, wherein the conductive lead is configured to causeelectron emission upon irradiation of the destructible laser target. 11.The structure of claim 7, further comprising a conductive lead at leastpartially located on at least one of the support structure and thehandling die.
 12. The structure of claim 1, wherein the piezoresistiveelement is located proximate to the destructible laser target.
 13. Thestructure of claim 12, wherein the piezoresistive element is located atleast one of above and below the destructible laser target.
 14. Thestructure of claim 1, wherein the piezoresistive element is configuredto facilitate application of an electric charge to the destructiblelaser target.
 15. The structure of claim 14, further configured tofacilitate application of the electric charge to the destructible lasertarget immediately prior to the time of irradiating the destructiblelaser target.
 16. The structure of claim 1, wherein the piezoresistiveelement is at least partially located on at least one of the supportstructure and the handling die.
 17. The structure of claim 16, whereinthe piezoresistive element is configured to facilitate application of anelectric current to the support structure.
 18. The structure of claim17, further configured to facilitate application of the electric currentto the support structure immediately prior to the time of irradiatingthe destructible laser target.
 19. The structure of claim 17, whereinthe piezoresistive element is configured to be heated upon applicationof the electric current.
 20. The structure of claim 1, wherein thepiezoresistive element is configured to influence types of particlesemitted upon irradiation of the destructible laser target.
 21. Thestructure of claim 20, wherein the piezoresistive element is configuredto cause electron emission upon irradiation of the destructible lasertarget.